Endoprostheses can be used to replace a missing biological structure, support a damaged biological structure, and/or enhance an existing biological structure. Frequently, only a temporary presence of the endoprosthesis in the body is necessary to fulfill the medical purpose. Surgical intervention to remove endoprostheses, however, can cause complications and may not even be possible. One approach for avoiding a permanent presence of all or part of an endoprosthesis is to form all or part of the endoprosthesis out of bioerodible material. The term “bioerodible” as used herein is understood as the sum of microbial procedures or processes solely caused by the presence of endoprosthesis within a body, which results in a gradual erosion of the structure formed of the bioerodible material.
At a specific time, the endoprosthesis, or at least the part of the endoprosthesis that includes the bioerodible material, loses its mechanical integrity. The erosion products are mainly absorbed by the body, although small residues can remain under certain conditions. A variety of different bioerodible polymers (both natural and synthetic) and bioerodible metals (particularly magnesium and iron) have been developed and are under consideration as candidate materials for particular types of endoprostheses. Although magnesium and magnesium alloys have been explored as candidate materials for bioerodible endoprostheses in the past, the mechanical and erosion properties of magnesium and magnesium alloys have presented certain difficulties that make the use of a bioerodible magnesium metal or alloy in certain endoprostheses, such as stents, impractical.